i was wondering what octane everyone else runs who's got a ported n/a.

before i had it ported, i ran 87 without problems.

now, i noticed my car started pinging (or at least what i think is a ping) when i let off the clutch in 1st from a stop. it sounds like a TICK or a TOONK sound and sometimes i can feel it on the stick.

at anyrate, i tried running rich with 87 octane and it still pinged. ran 89, same thing. when i switched to 91, i was able to run with my s-afc set ranging from -10 to -20 without pinging.

i'm just wondering if i'm alone on this one.

thanks,
john

 

Detonation only happens under load, so that's not what you're hearing. Perhaps you have a broken tranny/engine mount, or dying throwout bearing?

87 octane should be fine unless you are running a large timing advance. In an NA, always use the lowest octane available. The resistance to preigintion that higher octane provides is not necessay, and therefore it doesn't burn as well in an NA and leaves deposits.

 

damn you're quick....

it's not the mounts, i replaced them when i dropped in the new engine (prob 30k ago), so they should be fine. oh, i forgot to mention that it doesn't tick or toonk when i rev the engine up and then let off the clutch (like at about 2k rpm and let off normally).

if anything, it would be the bearing. my tranny already whines at idle and in all gears except 4th. whining goes away when i push in the clutch.

out of curiosity, what does detonation sound like?

thanks,
john

 

I just reread your post, and it seems that you are getting those noise when you put the engine under load. So it *might* be detonation. Pinging sounds like there are a bunch of little elves in your engine, banging on it with little hammers. Sort of a *tink,tinktinktinktinktink* sound for mild detonation, and a distinctive "*****!" for severe detonation.

I should mention that a streetported engine will require more fuel then a non-ported engine, so it is entirely possible (and not surprising) that you are running lean if you over-correct with your S-AFC.

 

Run 87 youll notice a difference!

 

I have experience pinging with my stock 89 GTU but only when it is over 90 degrees out and motor has been sitting in traffic. I have ran 87 in hi power portd motors before and it was fine except if I tried too much timing or really lean mixture. The extra timing and is not really worth the gain in response. I had 14 to 1 on ported motor and that helped compared to 11 or 12 to 1, but the extra timing did not do much. Stock map is usually rich so I am guessing the timing map is much advanced. You have a AFC so just play with it.

 

i think 92 works great in my n/a,completely stock,it runs cleaner and better over all with the higher grade of gas as well i noticed, runs perfect, you should always put the best gas in a rotary , remember the cheaper the gas the nastier it burns

 

the 'best' gas, would be a clean low octane (such as 87, i'm a chevron fan personally)

 

If you could get lower unleaded then you would want to put it in but the lowest is 87.

 

thanks for the input guys...i'll try toying with my safc more. when i had it set to no correction, i still had the "tick" and "toonk" sound. but it would just do it once when i let off the clutch..."tick" and then it would be fine.

i'll try setting it to +10% and see if it helps.

john

 

is it *only* when you release the clutch? or right as soon as you accelerate/begin to decelerate/etc? Doesn't sound right if it's only for a short few seconds, perhaps your u-joints are bad and they're clinking?

 

87. the closer you are to detonation, the more power an engine makes. and detonation has never been a problem i've heard of in n/a rotaries. i kinda wish we could get lower octane just to see some results. anyone running high octane (or low octane) have any results? i know i don't go to the dyno everytime i use a different octane gas, but if some were to have tests, proof is always nice. but until then, i'm going to continue using 87 (cheapest!) because i've never felt a difference using another octane (and i've had 5 gallons of 95 mixed in with about half a tank of gas). no other adjustments were made.

 

yep, only when i release the clutch starting out from a dead stop. other than that, i can redline in 2nd and it pulls strong all the way to 8k.

the tick sound definately sounds like it's coming from the exhaust...there's a hollow sound to it almost. like someone shot my exhaust with a bb gun. the toonk sound is like someone hit my exhaust with a rubber mallet.

if it's not pinging (which i'm still thinking it is) what else makes a big tick sound, but doesn't keep ticking?

john

 

could be that it's clanking against the heatshielding (mine does this), u-joints, all sorts of things can make a clink, but if the clink disappears immediatly after you get going, I'm doubting it's detonation, if it were pinging from the second you applied load, it'd just keep on pinging.

 

thanks sonic, i'm feeling better that it's not detonation, but i'll make an appt with the local rotatry god and let him take a listen to it just to be safe.

john